I needed a small portable headphone guitar amplifier that I could use for practicing when kids are asleep. Since my electronics knowledge is limited, I have picked up a kit based on TDA2822. It gives 1W with 12V. For an enclosure I have picked one that supports 9V battery from Mouser. Took me total of about 2 hours to put everything together. I am very happy with the final result. Amp works great and I can now jam without disturbing anybody in the house. Enclosure even has an optional clip in case I want to lift my butt from the chair and jam around the room.

I have removed the volume pot from the amp as my guitar has one built in (you can see jumpers on the PCB). Also the tip of the input jack is connected to both L and R channels on the amp as the guitar produces only mono sound. Switch cuts both + and - from the battery. As a finishing touch, I need to add some labels to the jacks so I know what's the in and what's the out. Same with the switch which needs on/off labels.